Dispersible fuel burner having a reverse gas flow flame stabilizer



Jam 239 1951 A P sAHA 2,539,165

DISPERSIBLE BRNER HAVING A REVERSE GAS FLOW FLAME STABILIZER Filed NOV.30, 1946 /NVENTO/2.

-AATTO P. SAHA H/S A T TORNEYS Patented an. 23, 1951 DISPERSIBLE FUELBURNER HAVING A RE- VERSE GAS FLOW FLAME STABILIZER Aatto P. Saha,Richmond County, N. Y., assignor,

by mesne assignments, to Cyclotherm Corporation, Oswego, N. Y., acorporation of New York Application November 30, 1946, Serial No.713,217

3 Claims. l

The present invention relates to a novel and improved apparatus foreffecting combustion of dispersible fuels.

The term dispersible fuel as hereinafter used in the specication and theclaims is intended to include solid fuels in powdered or pulverizedform, such as powdered coal, and fluid fuels, such as gaseous, vaporousand liquid fuels, for example, combustible gases and vapors as well ascombustible liquids such as fuel oils, capable of being atomized byspraying and the like.

Attempts have been made in the past to use luminous names, created byburning atomized fuel, for example, in air introduced under pressure toa combustion device, as a means of increasing the transfer of heat.While such methods are satisfactory, one diilculty has been that thellame front in the combustion device does not remain constant unless thedevice is carefully designed and operated, with the result that thellame front pulsates and thus causes an uneven transfer of heat andintermittent periods or cycles of incomplete combustion. This isparticularly true when a variable capacity nozzle is used.

The primary object of this invention is to provide an improved apparatusfor burning dispersible fuel in which substantially complete and perfectcombustion may be obtained with a stabilized, non-pulsating name andwhich has special utility in the firing of heat transmission apparatus,furnaces. boilers, and any other apparatus Where the object is thetransmission of the potential energy of fuel into useful heat.

Other objects of the invention are to provide an apparatus of simple,practical construction, dependable in operation, durable in use, andcapable of effecting substantial fuel economy due to efficiency andsimplicity in operation, and to provide an apparatus of this characterwhich is of compact and inexpensive construction.

Further objects of this invention will be apparent from a considerationof the description herein, especially when considered in connection withthe accompanying drawing hereinafter described.

According to the present invention, apparatus is provided in which theflow of the combustion supporting air and of the dispersible fuel aresuch as to insure the maintenance of a uniform flame and of constantheat emission conditions in the combustion space. The combustionsupporting air and the fuel within the apparatus are introduced into thecombustion chamber in relation to the flame stabilizer in such a manner66 that the combustion progresses at a constant rate throughout theapparatus for a given setting of air and fuel admission.

The combustion chamber and ame stabilizer provided in accordance withthis invention eliminates thel flash back of the ame to the fuel nozzle,such a flash back being a defect which at times may cause the apparatusto vibrate severely under exaggerated conditions. Hence, the apparatusof the present invention insures a constant name front and radiationemissivity for given conditions of operation and, therefore, results ina smooth operation and in constant flame temperatures for the entirecombustion space.

In operation, air is introduced so as to ilow through the combustionchamber in an annular, rotating air stream. This may be and preferablyis in the form of a substantially free spiral vortex, i, e., the air hasaxial as well as tangential velocity components. If the combustionchamber is divergent or convergent, the air will also have radialvelocity components within the combustion chamber. The axial flow of airWithin the combustion chamber is away from the zone or nozzle from whichthe fuel is introduced so that the axial components of motion of fueland air lare in the same direction. When air flows through thecombustion chamber in substantially the form of a whirling, annularstream or free spiral vortex, a cross section through the combustionchamber perpendicular to the longitudinal axis thereof shows an annularcross-section of air adjacent the Walls of the combustion chamber.Within this annular section there is a cylindrical zone referred tohereinafter in the specification and claims as a core. As will bedescribed hereinafter, this core serves as a suitable space fordispersing the fuel.

The dispersible fuel is injected preferably at one end of the apparatusthrough a nozzle which may, if desired, be of variable capacity. Thedispersible fuel ejected from the nozzle is dispersed through the flamestabilizer, to be describedpresently, and within the core of thewhirling, annular air stream.

The flame stabilizer is a substantially annular element proximate thefuel injection nozzle, and is designed to induce and maintain asecondary stream or iiow of material from the core through and aroundthe flame stabilizer. moving around the stabilizer has both axial andtangential velocity components and, if the ame stabilizer is divergentor convergent, also has radial velocity components. Unlike the air inthe The stream combustion chamber. however, the stream of materialwithin the flame stabilizer has an axial component of motion toward thefuel injection nozzle so that the flame stabilizer, in effect, acts as ameans to bring the flame toward the fuel injection nozzle. It isbelieved that the material flowing through the flame stabilizer towardthe nozzle is a mixture comprising unused air, unburned fuel particles,burned products, cracked fuel particles and possibility free hydrogen.

Although the invention is not limited thereto, the preferred embodimentof the invention contemplates that the source of air for the combustionchamber be the same as that for any air which forms part of thesecondary stream of material flowing through the flame stabilizer. Inthis embodiment the flame stabilizer is so positioned and constructedthat the flow of material through and around it is' induced by the flowof combustion supporting air into the combustion chamber.

In the continuous operation of the apparatus,

the fuel dispersed by means of a nozzle at one end of a combustionchamber is substantially completely burned when the fuel comes incontact with the surrounding atmosphere of combustion supporting air ina whirling, annular air stream which is ample in quantity and sodistributed as to insure complete combustion of the fuel. As a result ofsubstantially complete combustion, the flame is maintained at a maximumtemperature and a high degree of heat transmission by radiation andconvection is obtained.

Reference is now made more particularly to the accompanying drawingwherein;

Figure l is a view in longitudinal vertical section through a boilerwith which the combustion apparatus may be associated;

Figure 2 is a view in transverse section through the improved combustionapparatus taken on line 2-2 of Figure l, looking in the direction of thearrows;

Figure 3 is a View in transverse section taken on line 3 3 of Figure l;and

Figure 4 is a view in longitudinal vertical section through the intakeend of a combustion apparatus embodying the invention but having amodified form of flame stabilizer.

Referring now to the drawing, the combustion chamber designatedgenerally by reference numeral I lis shown incorporated in a boiler I2,it being understood, however, that the combustion chamber may beemployed in any apparatus used in heating. The walls I3 of combustionchamber II are preferably surfaces of revolution but other forms, forexample, polygonal in cross section may be used. Walls I3 may be ofmetal or refractory material or the like. The combustion chamber I I isusually cylindrical in form, but it may be conical with diverging orconverging walls, or it may be constructed to have a Venturi effect,such as by a shape approximating a hyperboloid of revolution. Anyvariation in the cross section of the chamber II is permissible if suchvariation is gradual so that sudden changes in the flow of materialstherein are avoided.

Combustion supporting air is introduced to combustion chamber I I so asto move therethrough in a whirling, annular air stream, such as insubstantially the form of a free vortex Il inside of which is a core I5, having an inner boundary I6, substantially free from flow ofcombustion supporting air other than that which may be introduced withthe fuel as a carrier therefor. The rotating air stream I4 may be formedby any means suitable for this purpose, such as volute I1. The core I5may be of any desired diameter depending upon the dimensions of voluteI'I and the combustion conditions as set by any suitable means forregulating the quantity of air and fuel introduced into the apparatus.It has been found that a core having a diameter of approximately 50 to90%, preferably from '75 to 85% of the diameter of combustion chamberiI, is quite effective for efficient operation.

The combustion supporting air introduced by means of volute I1 induces asuction effect in the openings I9 between the exterior wall of sleeve 24and the interior wall of a flame stabilizer 2i so as to draw throughthem a stream I8 of material from the interior of core I 5. As shown inFigure l, for example, stream I8 has within the flame stabilizer 2I anaxial component of motion toward fuel nozzle 22 within sleeve 24.Because of the momentum imparted by vortex I 4, this stream I8 may alsohave a tangential component around the inside of flame stabilizer 2 I,as shown in Figure 3. Upon leaving openings I9, stream I8 mingles withand becomes a part of the fresh stream 25 of combustion supporting airintroduced by volute I1.

The llame stabilizer 2I as shown in Figures l to 3 is cylindrical inshape and may be secured in position by any suitable means, such as bymeans of supports 26 attached to sleeve 24 or to wall 2l of volute I1.The dispersible fuel is introduced to the apparatus through nozzle 22,which may be a variable capacity nozzle, and is thereby dispersed in theform of a cone indicated by dotted lines 29 and 30. Initial ignition ofthe fuel dispersed Within this cone is accomplished by any well knownmeans, not shown. and not forming a part of the present invention. Onceignition has been accomplished, the temperature of the combustion issufficient to insure continual ignition of the fuel injected by nozzle22 and dispersed within cone 29, 30 and core I5. This continual ignitiontakes place initially within flame stabilizer 2I inasmuch as the flow ofair in stream I8, heated in combustion chamber II, carries the flameback to within close proximity of nozzle 22. The fuel which contacts theheated material in stream I8 is quickly heated to the ignitiontemperature, ignites, and stream I8, along with new products ofcombustion, is carried back (to the left in Figure l) through stabilizer2I, and emerges through openings I9 to mingle with the incoming stream25 of fresh, combustion supporting air. It is thus evident that llamestabilizer 2| not only has the primary function of stabilizing the flamewithin the apparatus by continually bringing the flame back to the endof the apparatus, but that it has the additional function of preheatingthe air stream 25 introduced to combustion chamber I I.

The fuel that is not ignited within flame stabilizer 2I passes to thecore I5, so that it is subjected to a thermal breakdown, yieldingparticles of free carbon that are heated to incandescence. When theseparticles of fuel come in contact with the air in the annular stream I4within combustion chamber II, they are burned very rapidly, thecombustion taking place primarily at boundary I6 between core I5 and airstream I4. The hot products of combustion diffuse into the air stream I4and are eliminated from combustion chamber II as the stream I4 exitsfrom end 32 of combustion chamber II. The combustion chamber may besimply left open at end 32 or may have associated therewith a volutecasing similar to volute I1 at the other end of the chamber, or maysimply have radial exit means such as designated by reference numeral 34in Figure 1.

The position and shape of the ame stabilizer may be varied in a greatmany ways without departing from the scope of this invention. It hasbeen found, however, that as a general principle it is preferable toposition the stabilizer coaxially with respect to the fuel nozzle andthe combustion chamber, and that the fuel nozzle should project into oneend of the stabilizer. as is shown by way of example in Figures 1 and 4of the drawing thus forming therewith an annular space in thestabilizer. It should be so placed with respect to the air introducingmeans, and so shaped, that it will induce and maintain a circulation ofair somewhat in the nature of an eddy current around the stabilizer aspreviously described. The stabilizer may have a circular or polygonalcross section and may have divergent or convergent walls. One example ofa flame stabilizer having divergent walls is the frustrum shaped amestabilizer 31 illustrated in Figure 4. It has been generally foundpreferab'e to make the overall cross section or diameter of the flamestabilizer somewhat smaller than the cross section or diameter of theconibustion chamber, and preferably just slightly smaller than the core.The specic method of supporting the flame stabilizer is optional, solong as the supporting means does not interfere substantially with theow of combustion supporting air 2U and is capable of withstanding theintense heat given olf by the burned fuel and the heated air passingthrough and around the supported end of the flame stabilizer.

As mentioned previously, Figure 4 illustrates a modification of theflame stabilizer wherein the stabilizer 31 has the shape of a hollowfrustrum, and is supported on sleeve 24 by means of spokelike supports26, as shown best in Figure 2. It will be noted that in thismodification, as in that shown in Figure l, the periphery of the cone ofdispersion of fuel from nozzle 22 does not intersect the walls of theame stabilizer, but that it does intersect the boundary between core l5and air stream iii within the combustion chamber il.

A great variety of devices may be used for forming whirling air streamli having a core l5. The devices shown in the drawing are merelyillustrative. It is to be understood, therefore, that the invention isnot limited to the specific mechanical construction of the vortexproducing means or other means for forming a whirling stream of air,shown in the drawing. It is also to be understood that any known meansfor varying the quantity oi air introduced and for varying the diameterof the core within the combustion chamber may be used without departingfrom thespirit of this invention.

If a solid fuel is to be used in accordance with the present invention,it is preferable to introduce it into the apparatus in powdered orpulverized form together with a suitable carrier such as air or an inertgas. If liquid fuel is to be burned it is likewise introduced into theapparatus generally in divided state. This may be effected by means ofan atomizer employing air, steam or fuel gas as the atomizing medium orby a mechanical atomizer. The atomized particles of liquid are vaporizedwithin the core and Within the stabilizer by the heat of combustion, andthe vapor is then burned in the same manner as though a gas had beenintroduced. If it is desired, liquid fuel may be vaporized before it isintroduced into the cores. If gaseous fuel is to be burned it may beintroduced through an orice at about the same position as the nozzle 22.

Any other device may be used for introducing powdered or pulverizedsolid fuel, liquid, vaporous or gaseous fuel without departing from thespirit of this invention.

The combustion apparatus herein described may be advantageously employedin connection with combustion chambers or furnaces in which the heatload varies. When the load is high a larger quantity of fuel isnecessarily consumed and a larger quantity of air must pass, through thecombustion chamber to support the increased combustion, The amount ofair passing through the vortex can be varied by altering the diameter ofthe core in any suitable manner. For example, with a high heat load asmaller core is used. In this case the mean axial velocity component ofthe air is greater and a larger quantity of air passes through thecombustion chamber.

Various modifications of this invention will be apparent to thoseskilled in the art and while every variation of the apparatus that maybe employed within the scope of this invention has not been illustrated,the invention is intended to include all such modifications as may beembraced within the following claims.

I claim:

1. An apparatus for burning dispersible fuel comprising in combination acombustion chamber having an interior surface of a substantiallycircular, transverse cross sectional shape to maintain substantially arotating, annular air stream therein and having an air inlet at one endthereof, means at the air inlet end of said combustion chamber having anend wall and formed to introduce air into the combustion chamber in theform of a rotating annular stream having a core, a nozzle forintroducing the dispersible fuel into said core, and flame stabilizingmeans for inducing a reverse ow of material from said core r toward saidnozzle, said flame stabilizing means comprising a substantially annularelement coaxial with the nozzle, open at both ends and having asubstantially circular cross section throughout its length, the minimuminternal diameter thereof being substantially greater than the externaldiameter of the nozzle, one open end of the element being adjacent, butspaced from, the end wall and the other open end thereof extendingsubLtantially to the combustion chamber, and said nozzle projectingthrough said end wall and said one open end into the element formingtherewith an annular space in the element for reverse flow of tnematerial into said other open end of the element, through the annularspace and out of said one open end to stabilize the flame.

2. An apparatus for burning dispersible fuel comprising in combination asubstantially cylindrical combustion chamber having an air inlet at oneend thereof, means at the air inlet end of said combustion chamberhaving an end wall and formed to introduce air into the combustionchamber in the form of a rotating annular stream having a core, a nozzlefor introducing and dispersing the dispersible fuel into the core ofsaid air stream, and flame stabilizing means for inducing a reverse owof material from said core toward said nozzle, said flame stabilizingmeans comprising a substantially cylindrical tubular element coaxialwith the nozzle, open at both endsand having an internal diametersubstantially greater than the external diameter of the nozzle, one openend of the tubular element being adjament, but spaced from. the end walland the other open end thereof extending substantially to the combustionchamber, and said nozzle projecting through said end wall and said oneopen end into the tubular element forming therewith an annular space inthe tubular element for reverse flow of said material into said otheropen end of the tubular element, through the annular space and out ofsaid one open end to stabilize the flame.

3. An apparatus for burning dispersible iuel comprising in combination asubstantially cylindrical combustion chamber having an air inlet at oneend thereof, means at the air inlet end of said combustion chamberhaving an end wall and formed to introduce air into the combustionchamber in the form of a rotating annular stream having a core, a nozzlefor introducing and dispersing the dispersible fuel into said core. andiiame stabilizing means for inducing a reverse ilow of material fromsaid core toward said nozzle, said flame stabilizing means comprising asubstantially annular element coaxial with the nozzle, open at bothends, and having substantially the shape of a hollow frustrum, thesmaller open end of the element being adjacent, but spaced from, the endwall and having an internal diameter substantially greater than theexternal diameter of the nozzle and the larger open end of the elementextending substantially to the combustion chamber, and said nozzleprojecting through said end wall and said smaller open end into theelement forming therewith an annular space in the element for reverseilow of said material into said larger open end of the element, throughsaid annular space and out of said smaller open end to stabilize thename.

AAI'IO P. SAHA.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,024,347 Light Apr. 23, 19121,437,300 Forster Nov. 28, 1922 1,618,808 Burg Feb. 22, 1927 1,679,830Lang Aug. 7, 1928 1,721,879 Hazlehurst et ai. July 23, 1929 1,878,926Yarrow Sept. 20, 1932 2,096,765 Saha Oct. 26, 1937 2,156,121 Macrae Apr.25, 1939 FOREIGN PATENTS Number Country Date 371,056 Great Britain Apr.21, 1932

